This invention relates to a getter device, and more particularly to a getter device arranged in an envelope of an electronic element to keep the envelope at a vacuum and a fluorescent display device including a getter device arranged in an envelope.
A conventional image display device including a field emission cathode is constructed, for example, in such a manner as shown in FIG. 9. More particularly, the conventional image display device generally designated at reference numeral 200 in FIG. 9 includes an envelope 201 formed by sealedly joining a cathode substrate 202 and an anode substrate 203 to each other through spacers 204. The cathode substrate 202 is provided on an inner surface thereof with a field emission cathode and correspondingly the anode substrate 203 is provided on an inner surface with a phosphor-deposited anode electrode acting as a display section in a manner to be opposite to the field emission cathode. In the image display device generally constructed as described above, the spacers 204 each are typically formed into a thickness as small as 500 .mu.m so that the field emission cathode and the anode electrode may be arranged while minimizing a distance therebetween. However, a conventional getter device 205 constituted by an annular getter vessel made of a metal material and having a getter material contained therein is generally formed into a thickness as large as several mm, so that the conventional image display device fails to arrange the getter device 205 in the envelope 201. In view of the fact, the conventional image display device, as shown in FIG. 9, employs a structure wherein a getter chamber member 206 of a box-like shape is arranged on a rear surface of the cathode substrate 202 of the envelope 201 and communicates through an evacuation hole 207 of a small size with the envelope 201. Then, the getter material is heated using suitable heating means externally arranged such as high-frequency heating or the like, resulting in being evaporated and then deposited on an inner surface of the getter chamber member 206 to form a getter mirror thereon.
As will be noted from the foregoing, the conventional getter device is disadvantageously increased in thickness, resulting in failing to be arranged in a narrow space. Thus, the conventional getter device causes the image display device which is an example of an electronic device having such a getter device incorporated therein to meet with disadvantages.
One of the disadvantages is that the image display device having a field emission cathode incorporated therein is featured in that the envelope is formed into a high thin configuration. However, mounting of the getter device on the envelope, as described above, causes the whole image display device to be substantially increased in thickness, to thereby deteriorate the above-described feature of the image display device.
Another disadvantage is that arrangement of the getter device 205 in the getter chamber member 206 additionally requires a step of providing the getter chamber member 206, leading to an increase in manufacturing cost.
The image display device, as described above, is so constructed that the getter device 205 is arranged in the getter chamber member 206 mounted on the envelope 201 and a getter film 208 and envelope 201 are permitted to communicate through the evacuation hole of a small size with each other. Unfortunately, in order to permit gas produced in the envelope 201 to be adsorbed on a getter film 208, such a construction causes the gas to be required to enter the getter chamber member 206 through the evacuation hole 207 of a small hole, leading to a decrease in efficiency of the getter device as compared with a construction wherein the getter film is formed directly on an inner surface of the envelope.
A further disadvantage countered with the conventional image display device is that a conventional deposition-type getter film formed in the getter device, when it loses activity once, is hard to be activated again, resulting in being gradually decreased in gas adsorbing capability with lapse of operation of the electronic device, resulting in a degree of vacuum of the device being deteriorated.
Still another problem is due to the construction of the conventional getter device that the getter material is charged in the getter vessel made of a metal material. The construction causes heating efficiency of the getter to be deteriorated.